Benign and malignant breast neoplasms are frequently surrounded by a dense collagen matrix which is absent in normal breast tissue. The objective of this study is to understand the role of the collagen matrix in the biological course of breast neoplasms. This abnormal collagen deposition will be characterized in human benign and malignant tumors and in the DMBA-induced rat breast cancer model. The rate of collagen and protein synthesis, soluble collagen, type of cell synthesizing collagen (fibroblast or neoplastic) will be determined. Correlation will be made with histology, clinical course, tumor size and metastases. The hypothesis that lack of collagen cross-linking increases virulence will be tested in rat mammary tumors using a cross-link inhibitor. The effects of endocrine manipulations on collagen and protein synthesis in the endocrine dependent DMBA rat tumor will be similarly examined.